The deeper you dig into Mexican cooking, the more addicted you get to the unique flavors and ingredients. A bunch of cilantro from the grocery store is fine but you start to crave more. Unfortunately, this means no spur of the moment trips to the store for your herbs. You normally will need plant them yourself. You may even get to the point where you grow your own corn for homemade tortillas. I did once!
Culantro (Eryngium foetidum)
We all know cilantro, or fresh coriander, but before the conquest, this unique flavor was provided by culantro. It's not as delicate and won't bolt in the summer the way cilantro does. I've tried growing cilantro and I like that it's stronger tasting than the store-bought but I found it a bother. Culantro, on the other hand, it's hardier and bolts at the end of the season, but reseeds itself easily so I'll have another supply the following Spring.
I've heard that in Mexico City, certain aficiandos insist on culantro for their tacos over cilantro. I'll leave that to the experts. I'm glad to have access.
Epazote (Dysphania ambrosioides)
Occasionally you find fresh epazote in the Mexican markets and once I even found it in my local mainstream supermarket, packed in plastic with the other herbs! I wouldn't be able to make it without a plant near my kitchen. Its most famous use is with beans, making them more digestible, it's said, but I think the real value is culinary. It's odd at first but it's great and you start wondering about new ways to use it. It's classic to put a leaf or two on a simple quesadilla but I love it with sauteed mushrooms or grilled octopus.
In Hidalgo, I've had it mixed with fried onions and ricotta cheese.
You can find it dried but personally I think it's as worthless as dried basil. It really deserves to be consumed fresh.
It can be invasive so I always grow it in a pot. It comes back every year.
Hoja Santa, Hierba Santa, Acuyo (Piper auritum)
This seems to be only available as a cutting so you need to meet a nice person from Oaxaca or do a web search. I've purchased it before online but my best pot is from a clipping. The plant has a slight root beer and anise flavor. This tastes much better than it sounds. If you read my blog, you know I love to wrap fish in it and it's an essential part of mole verde. You see it mostly in Oaxacan and Veracruzano cuisine. It likes a moist environment with indirect sun but it can be invasive under the right conditions.
Nopal (Opuntia ficus indica)
All this plant requires is excellent drainage, a sunny spot and occasional water and you will be well fed with cactus paddles for a vegetable and prickly pears as a fruit. I really don't understand why we don't embrace this wonderful plant more. I think they're beautiful and if you have a flair for the dramatic, consider a row of nopales alternating with red roses. I've seen it and it's pretty spectacular.
Papaloquelite (Porophyllum ruderale subsp. macrocephalum)
I wouldn't call this one essential unless you love the food of Puebla and the cemitas sandwich in particular. It's oily, strong and has the romantic flavors of gasoline and mint. It's nice chopped up on grilled meats with salt and garlic and it's essential to the Dagwood sandwich known as a cemita. It's not really key but I think you should know about it and it's easy to grow.